Even before the clear signs that something even more sinister could soon be afoot (check out,for example, the grim news from Donetsk in Ukraine’s east tonight) Russia’s creeping takeover of the Crimea had stirred up uncomfortable memories across Eastern Europe. To take just one example, the Soviet invasion of eastern Poland in September 1939 (the Germans had attacked from the west) was justified by Moscow, at least in part, as a move to protect the substantial Ukrainian and Byelorussian populations that lived there, and then supposedly legitimized by a vote that saw them “reunited” with their compatriots as their territories — including, ironically, today’s Lviv (formerly Polish Lwow) — were transferred to the Soviet Union.

And then, of course, there are the Baltics, also occupied by the Soviets courtesy of the deal that Stalin struck with Hitler.

As the Financial Times explained yesterday, this is more than a matter of an uncomfortable history:

Nato last week more than doubled the number of fighter jets stationed in Lithuania to 10, and Barack Obama, US president, reaffirmed the alliance’s principle of collective defence in a phone call with the three Baltic presidents at the weekend.

“There is this anxiety that this is not just about Crimea or Ukraine but maybe also concerns the Baltics. That worry is very strong. All the excuses used by Russia in Ukraine could be used in the Baltics,” says Kristi Raik, senior research fellow at the Finnish Institute of International Affairs.

Although grouped together, the three Baltic countries each have their own vulnerabilities to Russia. Estonia and Latvia both have large Russian minorities, accounting for about a quarter of their populations. In Latvia about a third of the 586,000 ethnic Russians are classed as “non-citizens”, a hazy legal status that Moscow has been keen to exploit. Russia’s ambassador to Riga recently caused a stir by stating that a proposal to make it easier for native Russians in former Soviet states to gain Russian citizenship would “save the Latvian non-citizens out of poverty”.

David Smith, a professor of Baltic history and politics at the University of Glasgow, says: “It is a pressure point. It is an issue that Russia has sought to manipulate very much for its own end. It has no intrinsic interest in the plight of the Russian minorities – it just sees them as a pawn in the bigger game.”

The question of the Russian minorities in Latvia and Estonia (and, no, contrary to what you may readinThe New Republic, they are not “persecuted” ), especially the non-citizen populations, is something that is likely to come into very sharp focus very soon. Of the two, I would guess that more populous Latvia (roughly 2 million people against Estonia’s 1.3 million) is the most likely venue for trouble-making. Its economy is shakier. It has the larger Russian minority. The Latvian capital, Riga, has a majority ethnic-Russian population, and its powerful mayor, Nils Usakovs, is of Russian descent. His Harmony Centre alliance (the single largest grouping in the Latvian parliament, although it remains in opposition there) draws most of its support from Russian speakers and reportedly enjoys close links with United Russia, the key regime party in Russia.

Latvia is, like the other two Baltic states, a member of NATO. Stirring things up there could lead to a very telling demonstration of what that membership actually means.